Big Radials Grumman Goose General Assessment (April 2022)

Heh, it is done by sound and feel when I fly.

And yeah, IME, the, “Auto” part just means it is in the ballpark.

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This was actually a thing back in the day. There was some WW2-vintage gizmo that would keep the mixture set to given performance parameters so the pilot (or flight engineer) wasn’t continually messing with the levers (and thus potentially killing an engine) during long, slow climbs. The DC-6, for example, as a similar thing.

Anyway, the AUTO RICH and AUTO LEAN positions here are intended to give the desired climb/cruise performance with respect to the trade-off between fuel efficiency and speed, whichever is more important to you at the time. I have no idea how these antique systems worked but, given that in modern planes this refers to being some number of degrees rich or lean of peak EGT, I suspect these auto systems used a thermostat sort of thing.

Thnx for this explanation. So I guess this it how it should work. It does change gradually as on any modern(ish) plane though…
I’m really trying to get the best settings for each altitude and the engine power curve diagram of the real JRF-6B POH is not really helping.

Well, what should be happening is that you put the mixtures in AUTO RICH when you start the the engines and leave them there the whole flight UNLESS you’re trying to skimp on fuel, in which case you switch to AUTO LEAN for the cruise (along with < 70% power) and descent but back to AUTO RICH for landing. You can fiddle with the MP and RPM but don’t have to worry about the mixture. And you use AUTO RICH on the ground or sea level because it supposedly accounts for local pressure better than full rich.

As you climb, MP falls off for a given throttle position and all the other engine parameters and vital signs change somewhat, too. That’s just how all the things react to being in thinner, colder air.

I would begin instead on pages 38-44 of the documentation that comes with the BR Goose. This gives recommended power settings for all phases of flight. These values are usually given in ranges but they’re pretty narrow so only a bit of experimentation is needed to get what you like the best.

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So here’s what I gleaned from browsing the interweb…

The carbs (or fuel injection pumps) had an aneroid bellows attached. This filled or collapsed based on the barometric pressure. A rod was attached to the bellows and its movement moved the rod in and out, adjusting the mixture in the carburetor (or injection pumps).

If you’ve ever worked on sidedraft carbs (think Strombergs or SUs) the principle is much the same. The tapered needle moves up or down to enrich or to lean the mixture based on vacuum (or manifold pressure.)

The bellows allows for changes in barometric pressure regardless of manifold pressure.

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Thanks for the explanation.

There is a bug with the left engine if we use a seaport.

The left engine cut itself after a few seconds, and we can’t run it again.

We have that with a friend.

Same here…

For me its not just when you start at a seaport (though that happens as well) but it also happens after about 30min of flight.

Alls well, gauges are all in the green & suddenly carb temp rises quickly & the left engine starts to sputter & will die regardless of what you do (lean/enrich/throttle down/throttle up).

Its a shame as a really enjoy this aircraft but with such limited flight time there is no reason to bring it out.

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This seems to be an issue of having cross feed ON. I’m not sure if that’s really realistic or not, but have noticed my fuel pressure doesn’t stay high enough on the left engine when I do (at least during warmup and taxi). Plus the checklists mentions a couple times to make sure crossfeed is off…